This invention relates to an optical semiconductor device for producing laser beam by light amplification due to stimulated emission of a ray which has same phase and same wavelength of incident ray.
In conventional semiconductor light amplifier, each electrode is respectively provided on each major surface of semiconductor regions, and intensity of electric current between these electrodes is uniform over an area through an incident end face and an emission end face on which non-reflective coatings are formed, accordingly current density or carrier density is uniform over an activation region.
In this type of semiconductor light amplifier, because a consuming rate of carrier is not uniform, the carrier becomes surplus at a portion closer to the incident end face, and the carriers become deficient at a portion closer to the emission end face.
If such a semiconductor light amplifier is applied as a semiconductor laser without forming non-reflective coatings on both the incident end and emission end faces, supply of carriers becomes deficient at both the end faces while the carrier becomes surplus in the vicinity of a central portion.
A technique for solving this problem is disclosed in Japanese Patent Publication No. 62-37909 in which one of the electrodes is divided into a plurality of elements, and different intensity of the electric current is applied between the divided elements and the other electrode through the incident end face to the emission end face.
In the above stated publication, a characteristic diagram is shown in FIG. 8 as semi-conductor light amplifier. As can be understood from FIG. 8, it is possible to heighten an optical output limit by controlling electric current densities J.sub.1 and J.sub.2 in relation to distribution of a photon density S.
In the case where one of the electrodes is divided and the carrier density is changed so as to gradually increase the photon density S from the incident side to the emission side, it is necessary to divided the electrode as finely as possible in order to realize characteristics of the device relating to the photon density S whereby the photon density S is continuously increased, as shown in FIG. 8. If the electrode is divided into two or three as in the case of an embodiment disclosed in the above stated publication, the photon density is obliged to become in a stepped fashion as shown in FIG. 9. Even if the electrode is divided more finely, the characteristics of the photon density is obliged to becomes stepped fashion not a little, and the carrier density distribution therefore tends to become disturbed so that a lateral transverse mode or light intensity distribution becomes unstable and that a output mode tends to change into a high-degree mode. In addition, it is extremely difficult, in terms of manufacture, to divide the electrode in a continuous approximation manner, and there is a need to provide a number of power sources corresponding to the number of divided electrodes, consequently an unit thereof becomes in a large size, and control of the unit is difficult.